source: branches/eraser6/Manager/DirectExecutor.cs @ 913

/* 
 * $Id$
 * Copyright 2008 The Eraser Project
 * Original Author: Joel Low <lowjoel@users.sourceforge.net>
 * Modified By: Kasra Nassiri <cjax@users.sourceforge.net> @17/10/2008
 * Modified By: 
 * 
 * This file is part of Eraser.
 * 
 * Eraser is free software: you can redistribute it and/or modify it under the
 * terms of the GNU General Public License as published by the Free Software
 * Foundation, either version 3 of the License, or (at your option) any later
 * version.
 * 
 * Eraser is distributed in the hope that it will be useful, but WITHOUT ANY
 * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
 * A PARTICULAR PURPOSE. See the GNU General Public License for more details.
 * 
 * A copy of the GNU General Public License can be found at
 * <http://www.gnu.org/licenses/>.
 */

using System;
using System.Collections.Generic;
using System.Collections.Specialized;
using System.Text;
using System.Threading;
using System.IO;

using Eraser.Util;
using System.Security.Principal;
using System.Runtime.Serialization;
using System.Runtime.Serialization.Formatters.Binary;

namespace Eraser.Manager
{
    /// <summary>
    /// The DirectExecutor class is used by the Eraser GUI directly when the program
    /// is run without the help of a Service.
    /// </summary>
    public class DirectExecutor : Executor
    {
        public DirectExecutor()
        {
            thread = new Thread(Main);
        }

        protected override void Dispose(bool disposing)
        {
            thread.Abort();
            schedulerInterrupt.Set();
            schedulerInterrupt.Close();
            base.Dispose(disposing);
        }

        public override void Run()
        {
            thread.CurrentUICulture = Thread.CurrentThread.CurrentUICulture;
            thread.Start();
        }

        public override void AddTask(Task task)
        {
            lock (unusedIdsLock)
            {
                if (unusedIds.Count != 0)
                {
                    task.ID = unusedIds[0];
                    unusedIds.RemoveAt(0);
                }
                else
                    task.ID = ++nextId;
            }

            //Set the executor of the task
            task.Executor = this;

            //Add the task to the set of tasks
            lock (tasksLock)
                tasks.Add(task.ID, task);

            //Call all the event handlers who registered to be notified of tasks
            //being added.
            OnTaskAdded(task);

            //If the task is scheduled to run now, break the waiting thread and
            //run it immediately
            if (task.Schedule == Schedule.RunNow)
            {
                QueueTask(task);
            }
            //If the task is scheduled, add the next execution time to the list
            //of schduled tasks.
            else if (task.Schedule != Schedule.RunOnRestart)
            {
                ScheduleTask(task);
            }
        }

        public override bool DeleteTask(uint taskId)
        {
            lock (tasksLock)
            {
                if (!tasks.ContainsKey(taskId))
                    return false;

                Task task = tasks[taskId];
                lock (unusedIdsLock)
                    unusedIds.Add(taskId);
                tasks.Remove(taskId);

                for (int i = 0; i != scheduledTasks.Count; )
                    if (scheduledTasks.Values[i].ID == taskId)
                        scheduledTasks.RemoveAt(i);
                    else
                        ++i;

                //Call all event handlers registered to be notified of task deletions.
                OnTaskDeleted(task);
            }

            return true;
        }

        public override void ReplaceTask(Task task)
        {
            lock (tasksLock)
            {
                //Replace the task in the global set
                if (!tasks.ContainsKey(task.ID))
                    return;

                tasks[task.ID] = task;

                //Then replace the task if it is in the queue
                for (int i = 0; i != scheduledTasks.Count; ++i)
                    if (scheduledTasks.Values[i].ID == task.ID)
                    {
                        scheduledTasks.RemoveAt(i);
                        if (task.Schedule is RecurringSchedule)
                            ScheduleTask(task);
                        else if (task.Schedule == Schedule.RunNow)
                            QueueTask(task);
                    }
            }
        }

        public override void QueueTask(Task task)
        {
            lock (tasksLock)
            {
                //Set the task variable to indicate that the task is already
                //waiting to be executed.
                task.Queued = true;

                //Queue the task to be run immediately.
                scheduledTasks.Add(DateTime.Now, task);
                schedulerInterrupt.Set();
            }
        }

        public override void ScheduleTask(Task task)
        {
            RecurringSchedule schedule = (RecurringSchedule)task.Schedule;
            if (schedule.MissedPreviousSchedule &&
                ManagerLibrary.Instance.Settings.ExecuteMissedTasksImmediately)
                //OK, we've missed the schedule and the user wants the thing
                //to follow up immediately.
                scheduledTasks.Add(DateTime.Now, task);
            else
                scheduledTasks.Add(schedule.NextRun, task);
        }

        public override void QueueRestartTasks()
        {
            lock (tasksLock)
            {
                foreach (Task task in tasks.Values)
                    if (task.Schedule == Schedule.RunOnRestart)
                        QueueTask(task);
            }
        }

        public override void CancelTask(Task task)
        {
            lock (currentTask)
            {
                if (currentTask == task)
                {
                    currentTask.Canceled = true;
                    return;
                }
            }

            lock (tasksLock)
                for (int i = 0; i != scheduledTasks.Count; ++i)
                    if (scheduledTasks.Values[i] == task)
                    {
                        scheduledTasks.RemoveAt(i);
                        return;
                    }

            throw new ArgumentOutOfRangeException(S._("The task to be cancelled must " +
                "either be currently executing or queued."));
        }

        public override Task GetTask(uint taskId)
        {
            lock (tasksLock)
            {
                if (!tasks.ContainsKey(taskId))
                    return null;
                return tasks[taskId];
            }
        }

        public override ICollection<Task> GetTasks()
        {
            lock (tasksLock)
            {
                Task[] result = new Task[tasks.Count];
                tasks.Values.CopyTo(result, 0);
                return new List<Task>(result);
            }
        }

        public override void SaveTaskList(Stream stream)
        {
            lock (tasksLock)
                new BinaryFormatter().Serialize(stream, tasks);
        }

        public override void LoadTaskList(Stream stream)
        {
            lock (tasksLock)
            {
                //Load the list into the dictionary
                tasks = (Dictionary<uint, Task>)new BinaryFormatter().Deserialize(stream);

                //Ignore the next portion if there are no tasks
                if (tasks.Count == 0)
                    return;

                lock (unusedIdsLock)
                {
                    //Find gaps in the numbering
                    nextId = 1;
                    foreach (uint id in tasks.Keys)
                    {
                        Task task = tasks[id];
                        task.Executor = this;
                        while (id > nextId)
                            unusedIds.Add(nextId++);
                        ++nextId;

                        //Check if the task is recurring. If it is, check if we missed it.
                        if (task.Schedule is RecurringSchedule)
                            ScheduleTask(task);
                    }

                    //Decrement the ID, since the next ID will be preincremented
                    //before use.
                    --nextId;
                }
            }
        }

        /// <summary>
        /// The thread entry point for this object. This object operates on a queue
        /// and hence the thread will sequentially execute tasks.
        /// </summary>
        private void Main()
        {
            //The waiting thread will utilize a polling loop to check for new
            //scheduled tasks. This will be checked every 30 seconds. However,
            //when the thread is waiting for a new task, it can be interrupted.
            while (thread.ThreadState != ThreadState.AbortRequested)
            {
                //Check for a new task
                Task task = null;
                lock (tasksLock)
                {
                    if (scheduledTasks.Count != 0 &&
                        (scheduledTasks.Values[0].Schedule == Schedule.RunNow ||
                         scheduledTasks.Keys[0] <= DateTime.Now))
                    {
                        task = scheduledTasks.Values[0];
                        scheduledTasks.RemoveAt(0);
                    }
                }

                if (task != null)
                {
                    //Set the currently executing task.
                    currentTask = task;

                    try
                    {
                        //Prevent the system from sleeping.
                        KernelAPI.SetThreadExecutionState(KernelAPI.EXECUTION_STATE.ES_CONTINUOUS |
                            KernelAPI.EXECUTION_STATE.ES_SYSTEM_REQUIRED);

                        //Broadcast the task started event.
                        task.Queued = false;
                        task.Canceled = false;
                        task.OnTaskStarted(new TaskEventArgs(task));
                        OnTaskProcessing(task);

                        //Start a new log session to separate this session's events
                        //from previous ones.
                        task.Log.NewSession();

                        //Run the task
                        TaskProgressManager progress = new TaskProgressManager(currentTask);
                        foreach (Task.ErasureTarget target in task.Targets)
                            try
                            {
                                progress.Event.CurrentTarget = target;
                                ++progress.Event.CurrentTargetIndex;
                                if (target is Task.UnusedSpace)
                                    EraseUnusedSpace(task, (Task.UnusedSpace)target, progress);
                                else if (target is Task.FilesystemObject)
                                    EraseFilesystemObject(task, (Task.FilesystemObject)target, progress);
                                else
                                    throw new ArgumentException(S._("Unknown erasure target."));
                            }
                            catch (FatalException)
                            {
                                throw;
                            }
                            catch (Exception e)
                            {
                                task.Log.Add(new LogEntry(e.Message, LogLevel.Error));
                            }
                    }
                    catch (FatalException e)
                    {
                        task.Log.Add(new LogEntry(e.Message, LogLevel.Fatal));
                    }
                    catch (Exception e)
                    {
                        task.Log.Add(new LogEntry(e.Message, LogLevel.Error));
                    }
                    finally
                    {
                        //Allow the system to sleep again.
                        KernelAPI.SetThreadExecutionState(KernelAPI.EXECUTION_STATE.ES_CONTINUOUS);

                        //If the task is a recurring task, reschedule it since we are done.
                        if (task.Schedule is RecurringSchedule)
                            ((RecurringSchedule)task.Schedule).Reschedule(DateTime.Now);

                        //If the task is an execute on restart task, it is only run
                        //once and can now be restored to an immediately executed task
                        if (task.Schedule == Schedule.RunOnRestart)
                            task.Schedule = Schedule.RunNow;

                        //And the task finished event.
                        task.OnTaskFinished(new TaskEventArgs(task));
                        OnTaskProcessed(currentTask);
                    }

                    currentTask = null;
                }

                //Wait for half a minute to check for the next scheduled task.
                schedulerInterrupt.WaitOne(30000, false);
            }
        }

        /// <summary>
        /// Manages the progress for any operation.
        /// </summary>
        private class ProgressManager
        {
            /// <summary>
            /// Starts measuring the speed of the task.
            /// </summary>
            public void Start()
            {
                startTime = DateTime.Now;
            }

            /// <summary>
            /// Tracks the amount of the operation completed.
            /// </summary>
            public long Completed
            {
                get
                {
                    return completed;
                }
                set
                {
                    lastCompleted += value - completed;
                    completed = value;
                }
            }

            /// <summary>
            /// The amount to reach before the operation completes.
            /// </summary>
            public long Total
            {
                get
                {
                    return total;
                }
                set
                {
                    total = value;
                }
            }

            /// <summary>
            /// Gets the percentage of the operation completed.
            /// </summary>
            public float Progress
            {
                get
                {
                    return (float)((double)Completed / Total);
                }
            }

            /// <summary>
            /// Computes the speed of the erase, in units of completion per second,
            /// based on the information collected in the previous 15 seconds.
            /// </summary>
            public int Speed
            {
                get
                {
                    if (DateTime.Now == startTime)
                        return 0;

                    if ((DateTime.Now - lastSpeedCalc).Seconds < 15 && lastSpeed != 0)
                        return lastSpeed;

                    lastSpeed = (int)(lastCompleted / (DateTime.Now - lastSpeedCalc).TotalSeconds);
                    lastSpeedCalc = DateTime.Now;
                    lastCompleted = 0;
                    return lastSpeed;
                }
            }

            /// <summary>
            /// Calculates the estimated amount of time left based on the total
            /// amount of information to erase and the current speed of the erase
            /// </summary>
            public TimeSpan TimeLeft
            {
                get
                {
                    if (Speed == 0)
                        return new TimeSpan(0, 0, -1);
                    return new TimeSpan(0, 0, (int)((Total - Completed) / Speed));
                }
            }

            /// <summary>
            /// The starting time of the operation, used to determine average speed.
            /// </summary>
            private DateTime startTime;

            /// <summary>
            /// The last time a speed calculation was computed so that speed is not
            /// computed too often.
            /// </summary>
            private DateTime lastSpeedCalc;

            /// <summary>
            /// The last calculated speed of the operation.
            /// </summary>
            private int lastSpeed;

            /// <summary>
            /// The amount of the operation completed since the last speed computation.
            /// </summary>
            private long lastCompleted;

            /// <summary>
            /// The amount of the operation completed.
            /// </summary>
            private long completed;

            /// <summary>
            /// The amount to reach before the operation is completed.
            /// </summary>
            private long total;
        }

        /// <summary>
        /// Provides a common interface to track the progress made by the Erase functions.
        /// </summary>
        private class TaskProgressManager : ProgressManager
        {
            /// <summary>
            /// Constructor.
            /// </summary>
            public TaskProgressManager(Task task)
            {
                foreach (Task.ErasureTarget target in task.Targets)
                    Total += target.TotalData;

                Event = new TaskProgressEventArgs(task);
                Start();
            }

            /// <summary>
            /// The TaskProgressEventArgs object representing the progress of the current
            /// task.
            /// </summary>
            public TaskProgressEventArgs Event
            {
                get
                {
                    return evt;
                }
                set
                {
                    evt = value;
                }
            }

            private TaskProgressEventArgs evt;
        }

        #region Unused Space erasure functions
        /// <summary>
        /// Executes a unused space erase.
        /// </summary>
        /// <param name="task">The task currently being executed</param>
        /// <param name="target">The target of the unused space erase.</param>
        /// <param name="progress">The progress manager object managing the progress of the task</param>
        private void EraseUnusedSpace(Task task, Task.UnusedSpace target, TaskProgressManager progress)
        {
            //Check for sufficient privileges to run the unused space erasure.
            if (!Permissions.IsAdministrator())
            {
                if (Environment.OSVersion.Platform == PlatformID.Win32NT &&
                    Environment.OSVersion.Version >= new Version(6, 0))
                {
                    throw new UnauthorizedAccessException(S._("The program does not have the required " +
                        "permissions to erase the unused space on disk. Run the program as an administrator " +
                        "and retry the operation."));
                }
                else
                    throw new UnauthorizedAccessException(S._("The program does not have the required permissions " +
                        "to erase the unused space on disk"));
            }

            //If the user is under disk quotas, log a warning message
            if (VolumeInfo.FromMountpoint(target.Drive).HasQuota)
                task.Log.Add(new LogEntry(S._("The drive which is having its unused space erased " +
                    "has disk quotas active. This will prevent the complete erasure of unused " +
                    "space and will pose a security concern"), LogLevel.Warning));

            //Get the erasure method if the user specified he wants the default.
            ErasureMethod method = target.Method;
            
            //Erase the cluster tips of every file on the drive.
            if (target.EraseClusterTips)
            {
                progress.Event.CurrentItemName = S._("Cluster tips");
                progress.Event.CurrentTargetTotalPasses = method.Passes;
                progress.Event.TimeLeft = progress.TimeLeft;
                task.OnProgressChanged(progress.Event);

                ProgressManager tipProgress = new ProgressManager();
                tipProgress.Start();
                EraseClusterTips(task, target, method,
                    delegate(int currentFile, string currentFilePath, int totalFiles)
                    {
                        tipProgress.Total = totalFiles;
                        tipProgress.Completed = currentFile;

                        progress.Event.CurrentItemName = S._("(Tips) {0}", currentFilePath);
                        progress.Event.CurrentItemProgress = tipProgress.Progress;
                        progress.Event.CurrentTargetProgress = progress.Event.CurrentItemProgress / 10;
                        progress.Event.TimeLeft = tipProgress.TimeLeft;
                        task.OnProgressChanged(progress.Event);

                        lock (currentTask)
                            if (currentTask.Canceled)
                                throw new FatalException(S._("The task was cancelled."));
                    }
                );
            }

            //Make a folder to dump our temporary files in
            DirectoryInfo info = new DirectoryInfo(target.Drive);
            VolumeInfo volInfo = VolumeInfo.FromMountpoint(target.Drive);
            FileSystem fsManager = FileSystem.Get(volInfo);
            info = info.CreateSubdirectory(FileSystem.GenerateRandomFileName(info, 18));

            try
            {
                //Set the folder's compression flag off since we want to use as much
                //space as possible
                if (Eraser.Util.File.IsCompressed(info.FullName))
                    Eraser.Util.File.SetCompression(info.FullName, false);

                //Continue creating files while there is free space.
                progress.Event.CurrentItemName = S._("Unused space");
                task.OnProgressChanged(progress.Event);
                while (volInfo.AvailableFreeSpace > 0)
                {
                    //Generate a non-existant file name
                    string currFile = FileSystem.GenerateRandomFileName(info, 18);

                    //Create the stream
                    using (FileStream stream = new FileStream(currFile, FileMode.CreateNew,
                        FileAccess.Write, FileShare.None, 8, FileOptions.WriteThrough))
                    {
                        //Set the length of the file to be the amount of free space left
                        //or the maximum size of one of these dumps.
                        long streamLength = Math.Min(ErasureMethod.FreeSpaceFileUnit,
                            volInfo.AvailableFreeSpace);

                        //Handle IO exceptions gracefully, because the filesystem
                        //may require more space than demanded by us for file allocation.
                        while (true)
                            try
                            {
                                stream.SetLength(streamLength);
                                break;
                            }
                            catch (IOException)
                            {
                                if (streamLength > volInfo.ClusterSize)
                                    streamLength -= volInfo.ClusterSize;
                                else
                                    throw;
                            }

                        //Then run the erase task
                        method.Erase(stream, long.MaxValue,
                            PrngManager.GetInstance(ManagerLibrary.Instance.Settings.ActivePrng),
                            delegate(long lastWritten, int currentPass)
                            {
                                progress.Completed += lastWritten;
                                progress.Event.CurrentItemPass = currentPass;
                                progress.Event.CurrentItemProgress = progress.Progress;
                                if (target.EraseClusterTips)
                                    progress.Event.CurrentTargetProgress = (float)
                                        (0.1f + progress.Event.CurrentItemProgress * 0.8f);
                                else
                                    progress.Event.CurrentTargetProgress = (float)
                                        (progress.Event.CurrentItemProgress * 0.9f);
                                progress.Event.TimeLeft = progress.TimeLeft;
                                task.OnProgressChanged(progress.Event);

                                lock (currentTask)
                                    if (currentTask.Canceled)
                                        throw new FatalException(S._("The task was cancelled."));
                            }
                        );
                    }
                }

                //Erase old resident file system table files
                progress.Event.CurrentItemName = S._("Old resident file system table files");
                task.OnProgressChanged(progress.Event);
                fsManager.EraseOldFileSystemResidentFiles(volInfo, method, null);
            }
            finally
            {
                //Remove the folder holding all our temporary files.
                progress.Event.CurrentItemName = S._("Removing temporary files");
                task.OnProgressChanged(progress.Event);
                fsManager.DeleteFolder(info);
            }

            //Then clean the old file system entries
            progress.Event.CurrentItemName = S._("Old file system entries");
            ProgressManager fsEntriesProgress = new ProgressManager();
            fsEntriesProgress.Start();
            fsManager.EraseDirectoryStructures(volInfo,
                delegate(int currentFile, int totalFiles)
                {
                    lock (currentTask)
                        if (currentTask.Canceled)
                            throw new FatalException(S._("The task was cancelled."));

                    //Compute the progress
                    fsEntriesProgress.Total = totalFiles;
                    fsEntriesProgress.Completed = currentFile;

                    //Set the event parameters, then broadcast the progress event.
                    progress.Event.TimeLeft = fsEntriesProgress.TimeLeft;
                    progress.Event.CurrentItemProgress = fsEntriesProgress.Progress;
                    progress.Event.CurrentTargetProgress = (float)(
                        0.9 + progress.Event.CurrentItemProgress / 10);
                    task.OnProgressChanged(progress.Event);
                }
            );
        }

        private delegate void SubFoldersHandler(DirectoryInfo info);
        private delegate void ClusterTipsEraseProgress(int currentFile,
            string currentFilePath, int totalFiles);

        private static void EraseClusterTips(Task task, Task.UnusedSpace target,
            ErasureMethod method, ClusterTipsEraseProgress callback)
        {
            //List all the files which can be erased.
            List<string> files = new List<string>();
            SubFoldersHandler subFolders = null;

            subFolders = delegate(DirectoryInfo info)
            {
                //Check if we've been cancelled
                if (task.Canceled)
                    throw new FatalException(S._("The task was cancelled."));

                try
                {
                    //Skip this directory if it is a reparse point
                    if ((info.Attributes & FileAttributes.ReparsePoint) != 0)
                    {
                        task.Log.Add(new LogEntry(S._("Files in {0} did not have their cluster " +
                            "tips erased because it is a hard link or a symbolic link.",
                            info.FullName), LogLevel.Information));
                        return;
                    }

                    foreach (FileInfo file in info.GetFiles())
                        if (Util.File.IsProtectedSystemFile(file.FullName))
                            task.Log.Add(new LogEntry(S._("{0} did not have its cluster tips " +
                                "erased, because it is a system file", file.FullName),
                                LogLevel.Information));
                        else if ((file.Attributes & FileAttributes.ReparsePoint) != 0)
                            task.Log.Add(new LogEntry(S._("{0} did not have its cluster tips " +
                                "erased because it is a hard link or a symbolic link.",
                                file.FullName), LogLevel.Information));
                        else if ((file.Attributes & FileAttributes.Compressed) != 0 ||
                            (file.Attributes & FileAttributes.Encrypted) != 0 ||
                            (file.Attributes & FileAttributes.SparseFile) != 0)
                        {
                            task.Log.Add(new LogEntry(S._("{0} did not have its cluster tips " +
                                "erased because it is compressed, encrypted or a sparse file.",
                                file.FullName), LogLevel.Information));
                        }
                        else
                        {
                            try
                            {
                                foreach (string i in Util.File.GetADSes(file))
                                    files.Add(file.FullName + ':' + i);

                                files.Add(file.FullName);
                            }
                            catch (IOException e)
                            {
                                task.Log.Add(new LogEntry(S._("{0} did not have its cluster tips erased " +
                                    "because of the following error: {1}", info.FullName, e.Message),
                                    LogLevel.Error));
                            }
                        }

                    foreach (DirectoryInfo subDirInfo in info.GetDirectories())
                        subFolders(subDirInfo);
                }
                catch (UnauthorizedAccessException e)
                {
                    task.Log.Add(new LogEntry(S._("{0} did not have its cluster tips erased " +
                        "because of the following error: {1}", info.FullName, e.Message),
                        LogLevel.Error));
                }
                catch (IOException e)
                {
                    task.Log.Add(new LogEntry(S._("{0} did not have its cluster tips erased " +
                        "because of the following error: {1}", info.FullName, e.Message),
                        LogLevel.Error));
                }
            };

            subFolders(new DirectoryInfo(target.Drive));

            //For every file, erase the cluster tips.
            for (int i = 0, j = files.Count; i != j; ++i)
            {
                //Get the file attributes for restoring later
                StreamInfo info = new StreamInfo(files[i]);
                FileAttributes fileAttr = info.Attributes;

                try
                {
                    //Reset the file attributes.
                    info.Attributes = FileAttributes.Normal;
                    EraseFileClusterTips(files[i], method);
                }
                catch (Exception e)
                {
                    task.Log.Add(new LogEntry(S._("{0} did not have its cluster tips erased. " +
                        "The error returned was: {1}", files[i], e.Message), LogLevel.Error));
                }
                finally
                {
                    info.Attributes = fileAttr;
                }
                callback(i, files[i], files.Count);
            }
        }

        /// <summary>
        /// Erases the cluster tips of the given file.
        /// </summary>
        /// <param name="file">The file to erase.</param>
        /// <param name="method">The erasure method to use.</param>
        private static void EraseFileClusterTips(string file, ErasureMethod method)
        {
            //Get the file access times
            StreamInfo streamInfo = new StreamInfo(file);
            DateTime lastAccess = DateTime.MinValue,
                     lastWrite = DateTime.MinValue,
                     created = DateTime.MinValue;
            //Create the stream, lengthen the file, then tell the erasure method
            //to erase the tips.
            using (FileStream stream = streamInfo.Open(FileMode.Open, FileAccess.Write,
                FileShare.None, FileOptions.WriteThrough))
            {
                long fileLength = stream.Length;
                long fileArea = GetFileArea(file);

                try
                {
                    //Get the file access times
                    FileInfo info = streamInfo.File;
                    if (info != null)
                    {
                        lastAccess = info.LastAccessTime;
                        lastWrite = info.LastWriteTime;
                        created = info.CreationTime;
                    }

                    stream.SetLength(fileArea);
                    stream.Seek(fileLength, SeekOrigin.Begin);

                    //Erase the file
                    method.Erase(stream, long.MaxValue, PrngManager.GetInstance(
                        ManagerLibrary.Instance.Settings.ActivePrng), null);
                }
                finally
                {
                    //Make sure the file is restored!
                    stream.SetLength(fileLength);
                }
            }

            //Set the file times
            FileInfo fileInfo = streamInfo.File;
            if (fileInfo != null)
            {
                fileInfo.LastAccessTime = lastAccess;
                fileInfo.LastWriteTime = lastWrite;
                fileInfo.CreationTime = created;
            }
        }
        #endregion

        #region Filesystem Object erasure functions
        /// <summary>
        /// Erases a file or folder on the volume.
        /// </summary>
        /// <param name="task">The task currently being processed.</param>
        /// <param name="target">The target of the erasure.</param>
        /// <param name="progress">The progress manager for the current task.</param>
        private void EraseFilesystemObject(Task task, Task.FilesystemObject target,
            TaskProgressManager progress)
        {
            //Retrieve the list of files to erase.
            long dataTotal = 0;
            List<string> paths = target.GetPaths(out dataTotal);

            //Get the erasure method if the user specified he wants the default.
            ErasureMethod method = target.Method;

            //Calculate the total amount of data required to finish the wipe.
            dataTotal = method.CalculateEraseDataSize(paths, dataTotal);

            //Iterate over every path, and erase the path.
            for (int i = 0; i < paths.Count; ++i)
            {
                //Update the task progress
                progress.Event.CurrentTargetProgress = i / (float)paths.Count;
                progress.Event.CurrentTarget = target;
                progress.Event.CurrentItemName = paths[i];
                progress.Event.CurrentItemProgress = 0;
                progress.Event.CurrentTargetTotalPasses = method.Passes;
                task.OnProgressChanged(progress.Event);
                
                //Get the filesystem provider to handle the secure file erasures
                StreamInfo info = new StreamInfo(paths[i]);
                FileSystem fsManager = FileSystem.Get(VolumeInfo.FromMountpoint(info.DirectoryName));

                //Remove the read-only flag, if it is set.
                bool isReadOnly = false;
                if (isReadOnly = info.IsReadOnly)
                    info.IsReadOnly = false;

                try
                {
                    //Make sure the file does not have any attributes which may affect
                    //the erasure process
                    if ((info.Attributes & FileAttributes.Compressed) != 0 || 
                        (info.Attributes & FileAttributes.Encrypted) != 0 ||
                        (info.Attributes & FileAttributes.SparseFile) != 0)
                    {
                        //Log the error
                        task.Log.Add(new LogEntry(S._("The file {0} could not be erased " +
                            "because the file was either compressed, encrypted or a sparse file.",
                            info.FullName), LogLevel.Error));
                    }

                    //Create the file stream, and call the erasure method to write to
                    //the stream.
                    using (FileStream strm = info.Open(FileMode.Open, FileAccess.Write,
                        FileShare.None, FileOptions.WriteThrough))
                    {
                        //Set the end of the stream after the wrap-round the cluster size
                        strm.SetLength(GetFileArea(paths[i]));

                        //If the stream is empty, there's nothing to overwrite. Continue
                        //to the next entry
                        if (strm.Length != 0)
                        {
                            //Then erase the file.
                            long itemWritten = 0,
                                 itemTotal = method.CalculateEraseDataSize(null, strm.Length);
                            method.Erase(strm, long.MaxValue,
                                PrngManager.GetInstance(ManagerLibrary.Instance.Settings.ActivePrng),
                                delegate(long lastWritten, int currentPass)
                                {
                                    dataTotal -= lastWritten;
                                    progress.Completed += lastWritten;
                                    progress.Event.CurrentItemPass = currentPass;
                                    progress.Event.CurrentItemProgress = (float)
                                        ((itemWritten += lastWritten) / (float)itemTotal);
                                    progress.Event.CurrentTargetProgress =
                                        (i + progress.Event.CurrentItemProgress) /
                                        (float)paths.Count;
                                    progress.Event.TimeLeft = progress.TimeLeft;
                                    task.OnProgressChanged(progress.Event);

                                    lock (currentTask)
                                        if (currentTask.Canceled)
                                            throw new FatalException(S._("The task was cancelled."));
                                }
                            );
                        }

                        //Set the length of the file to 0.
                        strm.Seek(0, SeekOrigin.Begin);
                        strm.SetLength(0);
                    }

                    //Remove the file.
                    FileInfo fileInfo = info.File;
                    if (fileInfo != null)
                        fsManager.DeleteFile(fileInfo);
                }
                catch (UnauthorizedAccessException)
                {
                    task.Log.Add(new LogEntry(S._("The file {0} could not be erased because the " +
                        "file's permissions prevent access to the file.", info.FullName),
                        LogLevel.Error));
                }
                catch (FileLoadException)
                {
                    task.Log.Add(new LogEntry(S._("The file {0} could not be erased because the " +
                        "file is currently in use.", info.FullName), LogLevel.Error));
                }
                finally
                {
                    //Re-set the read-only flag
                    info.IsReadOnly = isReadOnly;
                }
            }

            //If the user requested a folder removal, do it.
            if (target is Task.Folder)
            {
                progress.Event.CurrentItemName = S._("Removing folders...");
                task.OnProgressChanged(progress.Event);

                Task.Folder fldr = (Task.Folder)target;
                if (fldr.DeleteIfEmpty)
                {
                    FileSystem fsManager = FileSystem.Get(VolumeInfo.FromMountpoint(fldr.Path));
                    fsManager.DeleteFolder(new DirectoryInfo(fldr.Path));
                }
            }

            //If the user was erasing the recycle bin, clear the bin.
            if (target is Task.RecycleBin)
            {
                progress.Event.CurrentItemName = S._("Emptying recycle bin...");
                task.OnProgressChanged(progress.Event);

                ShellAPI.SHEmptyRecycleBin(IntPtr.Zero, null,
                    ShellAPI.SHEmptyRecycleBinFlags.SHERB_NOCONFIRMATION |
                    ShellAPI.SHEmptyRecycleBinFlags.SHERB_NOPROGRESSUI |
                    ShellAPI.SHEmptyRecycleBinFlags.SHERB_NOSOUND);
            }
        }

        /// <summary>
        /// Retrieves the size of the file on disk, calculated by the amount of
        /// clusters allocated by it.
        /// </summary>
        /// <param name="filePath">The path to the file.</param>
        /// <returns>The area of the file.</returns>
        private static long GetFileArea(string filePath)
        {
            StreamInfo info = new StreamInfo(filePath);
            VolumeInfo volume = VolumeInfo.FromMountpoint(info.Directory.FullName);
            long clusterSize = volume.ClusterSize;
            return (info.Length + (clusterSize - 1)) & ~(clusterSize - 1);
        }
        #endregion

        /// <summary>
        /// The thread object.
        /// </summary>
        private Thread thread;

        /// <summary>
        /// The lock preventing concurrent access for the tasks list and the
        /// tasks queue.
        /// </summary>
        private object tasksLock = new object();

        /// <summary>
        /// The list of tasks. Includes all immediate, reboot, and recurring tasks
        /// </summary>
        private Dictionary<uint, Task> tasks = new Dictionary<uint, Task>();

        /// <summary>
        /// The queue of tasks. This queue is executed when the first element's
        /// timestamp (the key) has been past. This list assumes that all tasks
        /// are sorted by timestamp, smallest one first.
        /// </summary>
        private SortedList<DateTime, Task> scheduledTasks =
            new SortedList<DateTime, Task>();

        /// <summary>
        /// The currently executing task.
        /// </summary>
        Task currentTask;

        /// <summary>
        /// The list of task IDs for recycling.
        /// </summary>
        private List<uint> unusedIds = new List<uint>();

        /// <summary>
        /// Lock preventing concurrent access for the IDs.
        /// </summary>
        private object unusedIdsLock = new object();

        /// <summary>
        /// Incrementing ID. This value is incremented by one every time an ID
        /// is required by no unused IDs remain.
        /// </summary>
        private uint nextId;

        /// <summary>
        /// An automatically reset event allowing the addition of new tasks to
        /// interrupt the thread's sleeping state waiting for the next recurring
        /// task to be due.
        /// </summary>
        AutoResetEvent schedulerInterrupt = new AutoResetEvent(true);
    }
}